U.S. patent number 5,369,786 [Application Number 07/694,153] was granted by the patent office on 1994-11-29 for enhanced power level usage in a radiotelephone system.
This patent grant is currently assigned to Motorola, Inc.. Invention is credited to Thomas G. Hulsebosch.
United States Patent |
5,369,786 |
Hulsebosch |
November 29, 1994 |
Enhanced power level usage in a radiotelephone system
Abstract
A radiotelephone system allows a subscriber unit (125) to
transmit above a predetermined maximum power level. The maximum
power level is set at a source base-station (130) and corresponds
to the maximum power level a subscriber unit (125) can transmit at
without subjecting neighboring target base-stations to
interference. When the received signal strength indication (RSSI)
of the subscriber unit (125) as measured by the source base-station
(130) falls below a transfer threshold, the radiotelephone system
determines if the subscriber unit (125) is in the best sector/cell.
If the subscriber unit (125) is in the best sector/cell, the
subscriber unit (125) is allowed to transmit at a power level above
the predetermined maximum to maintain communication to the source
base-station (130).
Inventors: |
Hulsebosch; Thomas G.
(Palatine, IL) |
Assignee: |
Motorola, Inc. (Schaumburg,
IL)
|
Family
ID: |
24787620 |
Appl.
No.: |
07/694,153 |
Filed: |
May 1, 1991 |
Current U.S.
Class: |
455/70; 455/522;
455/524; 455/127.2 |
Current CPC
Class: |
H04W
52/367 (20130101); H04W 52/243 (20130101) |
Current International
Class: |
H04Q
7/38 (20060101); H04B 007/26 () |
Field of
Search: |
;455/70,50.1,52.1,33,34,63,127,343,33.1,38.3,54.1,34.1,56.1,62,67.1,68,69
;379/63 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
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|
0372759 |
|
Nov 1989 |
|
EP |
|
2229609 |
|
Feb 1990 |
|
GB |
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Primary Examiner: Urban; Edward F.
Assistant Examiner: Pham; Chi
Attorney, Agent or Firm: Sonnentag; Richard A.
Claims
What I claim is:
1. A radiotelephone system having enhanced maximum power level
usage, the radiotelephone system having a source base-station
coupled to a plurality of target base-stations via a base-station
interface, the source base-station communicating with a subscriber
unit on a radio frequency (RF) channel, the source base-station
having the capability to instruct the subscriber unit to transmit
at at least one of a plurality of RF power levels, the source
base-station having a predetermined maximum subscriber unit
transmission level value (MAXPL) corresponding to a predetermined
subscriber unit RF power level that said subscriber unit is allowed
to transmit, said MAXPL being below the maximum subscriber unit RF
power level that said subscriber unit is capable to transmit, the
radiotelephone system comprising:
means, at the source base-station, for providing at least a first
communication transfer threshold;
means, at the source base-station, for measuring a first signal
quality value of a transmission from said subscriber unit on said
radio frequency channel;
means, at at least one target base-station, for measuring at least
a second signal quality value of a transmission from said
subscriber unit on said radio frequency channel;
means, at the base-station interface, for determining whether or
not said subscriber unit is in the best coverage area based on said
first signal quality value and said at least a second signal
quality value; and
means, at the source base-station, for instructing the subscriber
unit to transmit at a level above said MAXPL when said first signal
quality value is less than said at least a first communication
transfer threshold and if said subscriber unit is in the best
coverage area.
2. The radiotelephone system of claim 1 wherein said means for
measuring a first signal quality value further comprises means for
measuring a first signal strength value.
3. The radiotelephone system of claim 1 wherein said means for
measuring at least a second signal quality value further comprises
means for measuring at least a second signal strength value.
4. The radiotelephone system of claim 1 wherein said means for
determining further comprises means for providing a hysteresis
value correlating the physical location of the source base-station
to said at least one target base-station.
5. The radiotelephone system of claim 4 wherein said means for
determining further comprises means for adding said hysteresis
value to said first signal quality value to produce a first
modified signal quality value.
6. The radiotelephone system of claim 5 wherein said means for
determining further comprises means for determining whether or not
said subscriber unit is in the best coverage area based on said
first modified signal quality value and said at least a second
signal quality value.
7. A radiotelephone system having enhanced maximum power level
usage, the radiotelephone system having a source base-station
coupled to a plurality of target base-stations, the source
base-station communicating with a subscriber unit on a source
channel, the source base-station having the capability to instruct
the subscriber unit to transmit at at least one of a plurality of
RF power levels, the source base-station having a predetermined
maximum subscriber unit transmission level value (MAXPL)
corresponding to a predetermined subscriber unit RF power level
that said subscriber unit is allowed to transmit, said MAXPL being
below the maximum subscriber unit RF power level that said
subscriber unit is capable to transmit, the radiotelephone system
comprising:
means, at the source base-station, for providing at least a first
communication transfer threshold;
means, at a target base-station, for transmitting on at least a
first target channel;
means, at the subscriber unit, for measuring a first signal quality
value of a transmission on the source channel;
means, at the subscriber unit, for measuring at least a second
signal quality value of said transmission on said at least a first
target channel;
means, at the source base-station, for determining whether or not
said subscriber unit is in the best coverage area based on said
first signal quality value and said at least a second signal
quality value; and
means, at the source base-station, for instructing the subscriber
unit to transmit at a level above said MAXPL when said first signal
quality value is less than said at least a first communication
transfer threshold and if said subscriber unit is in the best
coverage area.
8. The radiotelephone system of claim 7 wherein said means for
measuring a first signal quality value further comprises means for
measuring a first signal strength value.
9. The radiotelephone system of claim 7 wherein said means for
measuring at least a second signal quality value further comprises
means for measuring at least a second signal strength value.
10. The radiotelephone system of claim 7 wherein said means for
determining further comprises means for providing a hysteresis
value correlating the physical location of the source base-station
to said at least one target base-station.
11. The radiotelephone system of claim 10 wherein said means for
determining further comprises means for adding said hysteresis
value to said first signal quality value to produce a first
modified signal quality value.
12. The radiotelephone system of claim 11 wherein said means for
determining further comprises means for determining whether or not
said subscriber unit is in the best coverage area based on said
first modified signal quality value and said at least a second
signal quality value.
13. A method of enhancing maximum power level usage in a
radiotelephone system, the radiotelephone system having a source
base-station coupled to a plurality of target base-stations via a
base-station interface, the source base-station communicating with
a subscriber unit on a radio frequency (RF) channel, the source
base-station having the capability to instruct the subscriber unit
to transmit at at least one of a plurality of RF power levels, the
source base-station having a predetermined maximum subscriber unit
transmission level value (MAXPL) corresponding to a predetermined
subscriber unit RF power level that said subscriber unit is allowed
to transmit, said MAXPL being below the maximum subscriber unit RF
power level that said subscriber unit is capable to transmit, the
method comprising the steps of:
providing, at the source base-station, at least a first
communication transfer threshold;
measuring, at the source base-station, a first signal quality value
of a transmission from said subscriber unit on said radio frequency
channel;
measuring, at at least one target base-station, at least a second
signal quality value of a transmission from said subscriber unit on
said radio frequency channel;
determining, at the base-station interface, whether or not said
subscriber unit is in the best coverage area based on said first
signal quality value and said at least a second signal quality
value; and
instructing, at the source base-station, the subscriber unit to
transmit at a level above said MAXPL when said first signal quality
value is less than said at least a first communication transfer
threshold and if said subscriber unit is in the best coverage
area.
14. The method of claim 13 wherein said step of measuring a first
signal quality value further comprises the step of measuring a
first signal strength value.
15. The method of claim 13 wherein said step of measuring at least
a second signal quality value further comprises the step of
measuring at least a second signal strength value.
16. The method of claim 13 wherein said step of determining further
comprises the step of providing a hysteresis value correlating the
physical location of the source base-station to said at least one
target base-station.
17. The method of claim 16 wherein said step of determining further
comprises the step of adding said hysteresis value to said first
signal quality value to produce a first modified signal quality
value.
18. The method of claim 17 wherein said step of determining further
comprises the step of determining whether or not said subscriber
unit is in the best coverage area based on said first modified
signal quality value and said at least a second signal quality
value.
19. A method of enhancing maximum power level usage in a
radiotelephone system, the radiotelephone system having a source
base-station coupled to a plurality of target base-stations, the
source base-station communicating with a subscriber unit on a
source channel, the source base-station having the capability to
instruct the subscriber unit to transmit at at least one of a
plurality of RF power levels, the source base-station having a
predetermined maximum subscriber unit transmission level value
(MAXPL) corresponding to a predetermined subscriber unit RF power
level that said subscriber unit is allowed to transmit, said MAXPL
being below the maximum subscriber unit RF power level that said
subscriber unit is capable to transmit, the method comprising the
steps of:
providing, at the source base-station, at least a first
communication transfer threshold;
transmitting, at a target base-station, on at least a first target
channel;
measuring, at the subscriber unit, a first signal quality value of
a transmission on the source channel;
measuring, at the subscriber unit, at least a second signal quality
value of said transmission on said at least a first target
channel;
determining, at the source base-station whether or not said
subscriber unit is in the best coverage area based on said first
signal quality value and said at least a second signal quality
value; and
instructing, at the source base-station, the subscriber unit to
transmit at a level above said MAXPL when said first signal quality
value is less than said at least a first communication transfer
threshold and if said subscriber unit is in the best coverage
area.
20. The method of claim 19 wherein said step of measuring a first
signal quality value further comprises the step of measuring a
first signal strength value.
21. The method of claim 19 wherein said step of measuring at least
a second signal quality value further comprises the step of
measuring at least a second signal strength value.
22. The method of claim 19 wherein said step of determining further
comprises the step of providing a hysteresis value correlating the
physical location of the source base-station to said at least one
target base-station.
23. The method of claim 22 wherein said step of determining further
comprises the step of adding said hysteresis value to said first
signal quality value to produce a first modified signal quality
value.
24. The method of claim 23 wherein said step of determining further
comprises the step of determining whether or not said subscriber
unit is in the best coverage area based on said first modified
signal quality value and said at least a second signal quality
value.
25. A radiotelephone system having enhanced maximum power level
usage, the radiotelephone system having a source base-station
communicating with a subscriber unit on a radio frequency (RF)
channel within a first sector, the source base-station having the
capability to instruct the subscriber unit to transmit at at least
one of a plurality of RF power levels, the source base-station
having a predetermined maximum subscriber unit transmission level
value (MAXPL) corresponding to a predetermined subscriber unit RF
power level that said subscriber unit is allowed to transmit, said
MAXPL being below the maximum capable subscriber unit RF power
level that said subscriber unit is capable to transmit, the
radiotelephone system comprising:
means, at the source base-station, for providing at least a first
communication transfer threshold;
means, at the source base-station, for measuring a first signal
quality value of a transmission from said subscriber unit on said
radio frequency channel within the first sector;
means, at at least one target base-station, for measuring at least
a second signal quality value of a transmission from said
subscriber unit on said radio frequency channel within a second
sector;
means, at a base-station interface, for determining whether or not
said subscriber unit is in the best sector based on said first
signal quality value and said at least a second signal quality
value; and
means for instructing the subscriber unit to transmit at a level
above said MAXPL when said first signal quality value is less than
said at least a first communication transfer threshold and if said
subscriber unit is in the best sector.
26. The radiotelephone system of claim 25 wherein said means for
determining whether or not said subscriber unit is in the best
sector may likewise occur at said source base-station.
27. A radiotelephone system having enhanced maximum power level
usage, the radiotelephone system having a source base-station
coupled to a plurality of target base-stations, the source
base-station communicating with a subscriber unit on a radio
frequency (RF) channel, the source base-station having the
capability to instruct the subscriber unit to transmit at at least
one of a plurality of RF power levels, the source base-station
having a predetermined maximum subscriber unit transmission level
value (MAXPL) corresponding to a predetermined subscriber unit RF
power level that said subscriber unit is allowed to transmit, said
MAXPL being below the maximum subscriber unit RF power level that
said subscriber unit is capable to transmit, the radiotelephone
system comprising:
means, at the source base-station, for providing at least a first
communication transfer threshold;
means, at the source base-station, for measuring a first signal
quality value of a transmission from said subscriber unit on said
radio frequency channel;
means, at at least one target base-station, for measuring at least
a second signal quality value of a transmission from said
subscriber unit on said radio frequency channel;
means for determining whether or not said subscriber unit is in the
best coverage area based on said first signal quality value and
said at least a second signal quality value; and
means, at the source base-station, for instructing the subscriber
unit to transmit at a level above said MAXPL when said first signal
quality value is less than said at least a first communication
transfer threshold and if said subscriber unit is in the best
coverage area.
Description
FIELD OF THE INVENTION
The invention relates generally to radiotelephone systems and more
specifically to radiotelephone systems requiring handoff to
maintain communication to a subscriber.
BACKGROUND OF THE INVENTION
In radiotelephone systems, subscribers transmit at multiple power
levels to maintain communication to a base-station as the
subscriber moves throughout a particular coverage area. The use of
multiple power levels is necessary because, as a subscriber moves
away from the base-station it is communicating with, its effective
received signal strength as measured by the base-station decreases.
When the received signal strength falls below a particular
threshold, the quality of communication may begin to degrade. To
avoid the degradation, the base-station will instruct the
subscriber to transmit at the next highest power level. This
effectively increases the received signal strength of the
subscriber transmission as measured by the base-station, thus
avoiding the signal quality degradation.
As reuse patterns become closer and closer together, a restriction
on the power level that the subscriber transmits is required. This
is typically accomplished by setting a parameter that defines the
maximum power level (MAXPL) the subscriber can transmit while it is
being serviced by the current source base-station in a given
sector/cell. The parameter is typically determined at the cell site
planning stages and is typically set so that the maximum allowable
power level that the subscriber is able to transmit at is below the
available power level of the subscriber. This is done so that the
subscriber causes the least amount of interference to neighboring
coverage areas during its transmission.
A problem arises however, when a subscriber goes into a somewhat
concealed infrastructure, a parking garage or a building for
example. Since the power level is restricted to the MAXPL level,
the probability of the subscriber being able to communicate to the
source base-station decreases. In addition, the MAXPL algorithm
used at the source base-station limits the power level all the
time, instead of only when the mobile is out of the coverage area
of the serving cell. This problem, initially implemented to
decrease interference between neighboring coverage areas, has lead
to an increased number of dropped calls.
Thus, a need exists for a radiotelephone system which allows the
subscriber to transmit above the MAXPL limit when the subscriber is
in the best sector/cell while still limiting the amount of
interference caused by the subscriber during typical radiotelephone
operation.
SUMMARY OF THE INVENTION
A radiotelephone system has enhanced maximum power level usage and
has a source base-station coupled to a plurality of target
base-stations via a base-station interface. The source base-station
communicates with a subscriber unit on a radio frequency (RF)
channel, has the capability to instruct the subscriber unit to
transmit at at least one of a plurality of RF power levels, and has
a predetermined maximum subscriber unit transmission level value
which corresponds to a predetermined subscriber unit RF power level
below the maximum subscriber unit RF power level. The
radiotelephone system provides, at the source base-station, at
least a first communication transfer threshold. The radiotelephone
system measures, at the source base-station, a first signal quality
value of a transmission on the radio frequency channel and also
measures, at at least one target base-station, at least a second
signal quality value of a transmission on the radio frequency
channel. The radiotelephone system determines, at the base-station
interface, an optimum signal quality value of the first signal
quality value and at least the second signal quality value, and
instructs, at the source base-station, the subscriber unit to
transmit at a level above the predetermined subscriber unit RF
power level when the first signal quality value is less .than at
least the first communication transfer threshold and when the first
signal quality value is the optimum signal quality value.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 generally depicts base-stations coupled to an EMX in a
radiotelephone system that may be used to employ the present
invention.
FIG. 2 generally depicts a schematic diagram of the source
base-site and the target base-sites shown in FIG. 1.
FIG. 3 generally depicts in flow diagram form how a radiotelephone
system increases a subscriber's power level above MAXPL in
accordance with the invention.
FIG. 4 generally depicts how a radiotelephone system without MAHO
determines if a subscriber is in the best coverage area.
FIG. 5 generally depicts how a radiotelephone system with MAHO
determines if a subscriber is in the best coverage area.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
FIG. 1 generally depicts a cellular network which may employ the
present invention. Cellular networks may incorporate as many
different cells as is required to accommodate the coverage area.
For example, a cell 100 typically covers only a small portion of
the total coverage area in large cellular systems. As the cellular
network grows in a particular coverage area, frequency reuse
becomes an important parameter that is used to accommodate all the
subscribers necessary. In some analog radiotelephone systems, a
supervisory audio tone (SAT) is used to distinguish two different
RF channels transmitting at the same frequencies in two different
cells. Returning to FIG. 1, a first coverage area or cell 100 using
a SAT.sub.1 is bounded by six neighboring cells, but only three
neighboring cells are used for explanation purposes. A second
coverage area, or neighboring cells 105, 110 have a SAT of
SAT.sub.2 while still another neighboring cell 115 has a SAT of
SAT.sub.3. Each of these cells has its own base-station, which is
required to communicate to a subscriber 125. In the source cell
100, a source base-station 130 communicates to a subscriber 125 on
a source channel, which is a radio frequency (RF) signal at a
particular frequency. SAT.sub.1 is modulated on the RF signal by
the source base-station 130 and is demodulated by the subscriber
125. SAT.sub.1 is used by the subscriber 125 to identify the source
cell 100 the subscriber 125 is located within. In sectorized cells
(not shown), a similar method of communication transfer (called a
port change) is used when the subscriber 125 moves from sector to
sector within a given cell.
Each base-station within a particular cell in a cellular network is
connected to an EMX 120 switch, available from Motorola, Inc. and
described in Motorola Instruction Manual No. 68P81054E59 published
by Motorola Service Publications, Schaumburg, IL. The EMX 120, and
more particularly the three party circuit (not shown) in the EMX
120, is the interface between the base-stations within the cells
and the public switched telephone network (PSTN), which is the
land-line system. The EMX 120 also serves as a junction point
between base-stations in a cellular network. For example, as the
subscriber moves throughout the source cell 100, the base-station
130 continuously monitors the received signal strength indication
(RSSI) of the subscriber 125. As the subscriber 125 moves away from
the base-station 130, the RSSI of the subscriber 125 eventually
falls below a transfer threshold. The source base-station 130, via
the EMX 120, sends a message, which includes the source RSSI
measurement, to all neighboring cells, but again for the example
only neighboring cells 105, 110 are used. If target base-stations
135, 140 receive the transmission of the subscriber 125 and if the
handoff criterion is met for the particular cell 105, 110, the
target base-stations 135, 140 will send a response to the EMX 120
noting such. Target base-station 135, 140 will meet the handoff
criterion if the RSSI measured at the target base-stations 135,
140, plus some hysteresis value is greater than the RSSI measured
by the source base-station 130. The hysteresis value is used by
neighboring base-stations 135, 140 in part to take into account the
physically different locations of the target base-stations 135, 140
with respect to the source base-station 130. In addition, to ensure
that the target base-station 135, 140 RSSI is noticeably better
than the source base-station 130 RSSI, the hysteresis value is
added to the target base-station 135, 140 RSSI before the
comparison is made.
Each of the base-stations 130, 135, 140, 145, and 150 includes a
plurality of transmitters and receivers for operating on at least
one duplex signalling channel and a plurality of duplex voice
channels. One conventional analog system employs transmitters and
receivers of the type described in Motorola Instruction Manual No.
68P81058E32-A published by Motorola Service Publications,
Schaumburg, Ill., in 1989. The use of mobile assisted handoff
(MAHO) is particularly applicable to digital cellular systems.
Several of the systems that incorporate MAHO are the United States
Digital Cellular System (USDC) defined in EIA/TIA, Project Number
2215 titled "Dual--Mode Mobile Station--Base-station Compatibility
Standard" dated Dec. 1989, the Japan Digital Cellular Standard
(JDC) defined by the Research and Development Center for Radio
Systems in Japan (RCR), dated Jan. 1991, and the Groupe Special
Mobile (GSM) Pan European Digital Cellular System defined in the
GSM Recommendations. As is the case in analog cellular systems,
digital cellular systems use a cell identification value. Several
such digital cellular systems use a digital voice colour code
(DVCC). In the preferred embodiment, up to 256 DVCC's are
available. Thus, in a given cellular coverage area, each cell has a
distinct DVCC associated to a corresponding base-station. When the
base-station transmits a broadcast signal throughout its coverage
area, the broadcast signal has the DVCC value modulated on it. This
concept is similar to the SAT concept used in analog cellular.
FIG. 2 generally depicts a block diagram of a base-station used to
implement the present invention. FIG. 2 depicts the source
base-station 130 but may also be used to generally depict all
base-stations, as shown in FIG. 1. An interface 200 connects the
base-station 130 to the EMX 120. The interface 200 is coupled to a
processor, which in the preferred embodiment is a Motorola 68030
microprocessor. The processor 205 is also coupled to a memory block
210, which includes RAM and ROM. The processor 205 is coupled to a
transmitter/receiver 220 which interfaces between the processor and
the channel being transmitted by the base-station 130. Data
entering the base-station 130 from the EMX 120 is input into the
interface 200 and sent to the processor 205. The processor 205
accesses the memory 210 to retrieve the required
calibration/hysteresis factors necessary for transmission and
reception. The processor 205 sends the data to the
transmitter/receiver 220, where the information is modulated onto a
RF channel and transmitted to the subscriber unit 125.
Current radiotelephone systems limit the maximum power level
transmitted by the subscriber to a level below the maximum power
level that the subscriber unit 125 is capable of transmitting in.
The MAXPL parameter was set below the maximum capable power level
because interference would increase if the subscriber unit 125 were
allowed to transmit at its maximum capable power level. For very
dense coverage areas, this interference could potentially lead to
an increase in dropped calls. The problem with the MAXPL parameter
is that it limits the power level at all times. Logically, however,
if the subscriber unit 125 is in the best sector/cell at the time
where a power level increase is required, and the subscriber is at
MAXPL, an increase in the subscriber unit 125 power level should
not affect neighboring sectors/cells. Thus, allowing a subscriber
unit 125 to transmit at a power level above MAXPL will not increase
interference with neighboring sector/cells if, at the time the
power increase is required, the subscriber unit 125 is in the
optimum or best sector/cell.
FIG. 3 generally depicts the steps a radiotelephone system
undergoes to increase the subscriber power level above MAXPL in
accordance with the invention. The process starts at 300 when the
source base-station 130 measures at 303 the subscriber unit RSSI. A
test is then performed at 306 to determine if the RSSI is above the
transfer threshold. In the preferred embodiment, the transfer
threshold is the power change threshold used to vary the subscriber
unit 125 power level. If it is, the test at 303 is repeated. If the
measured RSSI is not above the transfer threshold, a test is
performed at 309 to determine if the subscriber unit 125 is in the
best coverage area. If it is, the source base-station 130 increases
at 321 the subscriber power level above the MAXPL if necessary. If
the subscriber unit 125 is not in the best coverage area, a test is
performed at 312 to determine if the subscriber units power level
is currently below MAXPL. If it is, the source base-station 130
will increase at 315 the subscriber power level up to, but not
exceeding, MAXPL. If the subscriber unit 125 is currently
transmitting at or above MAXPL and the subscriber unit 125 is not
in the best coverage area, the source base-station will do nothing
318.
FIG. 4 generally depicts how a radiotelephone system without MAHO
determines if the subscriber unit 125 is in the best coverage area
as shown in step 309. This process starts at 400 when the source
base-station determines at 403 if the subscriber unit is in the
best sector of the source cell. A test is then performed at 406 to
determine if the subscriber unit is in the best sector. If it is
not, a determination is made at 409 that the subscriber unit is not
in the best coverage area. If, however, the subscriber unit 125 is
in the best sector, the source base-station 130 will send at 412 a
hand-off request (HOR) to the base-station interface 120. The
base-station interface 120 then sends at 415 an RSSI measurement
request to neighboring target base-stations. The target
base-stations measure at 418 the subscriber unit 125 RSSI and add
the corresponding hysteresis value for each particular target
base-station to the measured RSSI. A test is then performed at 420
to determine if the measured RSSI plus hysteresis for a target
base-station is greater than the source RSSI. If it is not, the
process stops at 421 at the particular target base-station. If the
measured RSSI plus hysteresis for a target base-station is greater
than the source RSSI, the target base-station reports at 422 a
response back to the base-station interface 120. A test is then
performed at 425 by the base-station interface 120 to determined if
any target base-stations responded. If any did respond, the
subscriber unit 125 is not in the best coverage area 427. If,
however, no target base-stations responded, the subscriber unit 125
is in the best coverage area 430.
FIG. 5 generally depicts how a radiotelephone system with MAHO
determines if the subscriber unit 125 is in the best coverage area
as shown in step 309. This process starts at 500 when the source
base-station determines at 503 if the subscriber unit is in the
best sector of the source cell. A test is then performed at 506 to
determine if the subscriber unit is in the best sector. If it is
not, a determination is made at 509 that the subscriber unit is not
in the best coverage area. If, however, the subscriber unit 125 is
in the best sector, the source base-station 130 will instruct at
512 the subscriber unit 125 to measure RSSI of neighboring target
base-stations. The subscriber unit 125 then measures at 515 the
RSSI of neighboring target base-stations. After the measurement,
the subscriber unit 125 responds at 518 back to the source
base-station 130 with the measured RSSI's. In an alternate
embodiment, the subscriber unit 125 may determine the best of the
measured RSSI's and respond back to the source base-station with
only that RSSI. Continuing, the source base-station 130 adds at 521
the corresponding hysteresis value for each particular target
base-station to the measured target base-station RSSI's. A test is
then performed at 524 to determine if any of the measured RSSI plus
hysteresis for any target base-station is greater than the source
RSSI. If there are target RSSI plus hysteresis values greater than
the source RSSI, the subscriber unit 125 is not in the best
coverage area 527. If, however, the source RSSI is greater than all
the RSSI plus hysteresis values, the subscriber unit 125 is in fact
in the best coverage area 530.
By determining if the subscriber unit 125 is in the best
sector/cell, the subscriber unit 125 is able to transmit above the
predetermined MAXPL level set at the source base-station 130. In
this manner, the subscriber unit 125 is able to maintain
communication with the source base-station 130 without subjecting
neighboring target base-stations to additional interference caused
by high level subscriber transmission.
* * * * *